We used salinity information for modeling habitats for coastal fishes (bluefish,
winter flounder) and for the horseshoe crab. The limited information available
for this wide geographic area, the dynamic nature of salinity in coastal
areas, and the tolerance ranges of most estuarine, freshwater, and marine
organisms dictated that the coverage deal with relatively broad but ecologically
meaningful salinity zones.

Available wide-scale digital information included annual average salinity
conditions characterizing tidal fresh, mixing, and seawater zones of East
Coast estuaries, from the NOAA Sea Division. This information was at a 1:250,000
scale. Higher resolution information was overlaid, including 1:24,000
characterizations of fresh, estuarine, and marine zones from aerial
photo-interpretation by the USFWS National Wetland Inventory, and by Maine
Geological Survey (Coastal Marine Geologic Environments). We also used the
Larsen and Doggett (1978) data for Maine estuaries. This verified or improved
upstream and downstream limits for the salinity zones in a number of Maine
rivers. More detailed data were available from our previous Great Bay, New
Hampshire, and Casco Bay, Maine, studies (Banner and Libby 1995, Banner and
Hayes 1996), and from coverages developed for habitat suitability modeling
for several marine species in Casco Bay and Sheepscot Bay, Maine (Brown et
al. 2000).

National Wetland Inventory characterizations of marine ( M*) were used to
designate areas as 25 to 35 ppt (saline); areas designated as estuarine (E*)
were regarded as 5 to 25 ppt (mixing zone); tidally influenced and interior
wetlands were regarded as fresh. These coverages were revised to eliminate
impounded or isolated wetlands, and to add or remove river segments, based
on Coastal Marine Geologic Environments coverages, salinity surveys, or local
knowledge.

The polygon coverages were converted to grids, then combined with salinity
grids from earlier works (Casco Bay, Sheepscot Bay, Great Bay), as a Gulf
of Maine salinity grid.

Sources

Banner, A. and G. Hayes. 1996. Important Habitats of Coastal New Hampshire.
Falmouth Maine: U.S. Fish and Wildlife Service Gulf of Maine Project. 77pp.